We describe a rare case of a 4-month-old girl presenting with a several month history of reduced movement to the left arm accompanied by a maculopapular rash to the limbs. X-ray findings included inflammatory periosteal changes to the radius and ulna. Treponema pallidum IgM was detected in both baby and mother, and a diagnosis of congenital syphilis was made. This case is an interesting clinical picture with a variety of important differential diagnoses, including non-accidental injury, malignancy, autoimmune disease and other congenital infections. With an increasing rate of congenital syphilis infection in the developed world, it is vital that clinicians are able to recognise symptoms to ensure prompt diagnosis and treatment. In this respect, we can attempt to avoid the chronic and potentially life-threatening complications of untreated infection.